1. Field Of The Invention
This invention relates generally to laser diode assemblies. More specifically, it pertains to a temperature regulating laser diode assembly having a thermoelectric cooling unit for permitting operation of the laser diode in harsh environmental conditions.
2. Description Of Related Art
Laser diodes have become preferred electronic components for applications requiring an inexpensive source of coherent light. Laser diodes, otherwise known as semiconductor lasers, are ideal for highly accurate optical information collection, transmission and processing. As the power and efficiency of laser diodes have increased, the variety of uses for laser diodes has greatly expanded. Once used solely for scientific and research applications, laser diodes are now employed in many commercial and consumer products.
The bar code scanner identification industry, in particular, uses laser diodes in many applications that require small, low-power laser scanners. Scanners using laser diodes are smaller, lighter and draw less power than helium-neon based laser scanners, which were previously the most commonly used type of laser scanner. As laser diode scanners have become more popular, they have been used in a variety of wide-ranging scanning applications including point-of-sale checkout terminals, assembly and production line tracking systems, and warehouse storage systems.
Depending upon the particular application, laser diode scanners may be subject to harsh environmental conditions that are less than ideal for electronic components, including high temperature and high humidity environments. Operating a laser diode at elevated temperatures for extended periods of time decreases the expected operating life of the component, thereby increasing maintenance costs and associated down-time of the scanning system.
Present scanning systems utilize thermoelectric coolers to remove heat from a laser diode, thereby reducing the temperature and preventing thermal degradation of the diode. A typical scanning device which employs a laser diode and a thermoelectric cooler is shown in FIG. 1. This system includes a laser diode 10 which is mounted on a retainer plate 12. The plate 12 is supported by a thermally conductive spacer 14 which is coupled to a thermoelectric cooler 16. A thermally conductive flange 18 holds an optical assembly 20 in a supported relationship with the diode 10 via two screws 19. Since the optical assembly 20 and the laser diode 10 are coupled by thermally conductive materials, they are maintained at the same temperature. A thermistor 24 detects the temperature of the spacer 14 and regulates the thermoelectric cooler 16 to keep the optical assembly 20 and laser diode 10 at a desired operating temperature. The laser diode 10 and the optical assembly 20 are hermetically sealed in a thermally insulated housing 22, which has an optically transparent window 26 for permitting the laser beam to exit.
Although present assemblies compensate for high ambient temperatures, they require coolers with sufficient capacity to cool the entire assembly. Additionally, these systems require complete thermal isolation of internal electronic components from the ambient environment, resulting in scanning systems that are bulky and inefficient.
When a laser diode is cooled below the temperature of the ambient environment, condensation may form on the laser diode window. Although a small heating element may be used to heat the window and prevent the formation of condensation, this further reduces the efficiency and increases the size of the scanning system.
Accordingly, there exists a need for a laser diode assembly that efficiently maintains the laser diode at the recommended operating temperature while preventing condensation from forming on the laser diode window.